The present invention relates to an electrical circuit having a switchable lockout feature whereby a primary operator can selectively enable or disable an auxiliary operator's ability to operate an actuator also controllable by the primary operator. While a circuit in accordance with the invention has many uses, it is particularly well suited to raising and lowering power windows in passenger vehicles.
Many passenger vehicles are equipped with power window systems. The windows in many such systems are operated by double pole double throw rocker switches. Throwing (i.e., activating) the rocker switch in one direction raises the corresponding window and activating it in the other lowers that window. A passenger is provided with an auxiliary switch that operates his or her own window. The driver, on the other hand, is provided with a driver's window switch and a plurality of primary switches to operate each of the passenger windows. Oftentimes, the driver is also provided with a separate lockout switch to prevent the passengers from operating their respective windows. When activated, these lockout switches still allow the driver to operate the windows no longer operable by the passengers.
FIG. 1 shows a schematic of a simplified prior art power window system having, for the purposes of explanation, only a single passenger window. The driver's switchplate 10 includes a normally closed lockout switch 12 with which the driver may disable the passenger's auxiliary switch 20. The driver's switchplate 10 also has a primary switch 14 to operate the passenger's bi-directional window motor 28. When the lockout switch 12 is closed, the auxiliary switch power terminal 22 is supplied with power. The auxiliary switch 20 may then be operated by the passenger to raise or lower the window. On the other hand, when the lockout switch 12 is open, power is not supplied to the auxiliary switch power terminal 22 and the passenger cannot operate the window.
The driver's ability to operate the passenger's window is independent of the setting of the lockout switch 14. This is because the driver's primary switch 14 supplies power to the passenger's window through an alternate path, using primary switch power terminal 18 which provides power as long as the ignition is on. A driver wishing to operate the passenger's window activates the primary switch 14, which outputs current through primary switch power terminal 18, through one of the normally closed auxiliary switch contacts 24, 26, through the window motor 28, through the other of the normally closed auxiliary switch contacts 24, 26 and then on to ground.
The power window system described above has a number of drawbacks. One of these is that a passenger can interfere with the driver's operation of the passenger's window even when the lockout switch 12 has been activated (opened). This is because electrical continuity must be maintained between the auxiliary switch contacts 24, 26 for the driver to operate the passenger's window. If a passenger were to fiddle with the auxiliary switch 20, he or she would break this continuity and thus interfere with the driver's operation of the passenger's window.
Another problem with the prior art window control circuits is that the power to operate a passenger's window passes through a driver's switchplate, imposing requirements which increase their cost and complexity. One such requirement is that a bi-directional window motor needs a current on the order of 10 to 20 amperes. This requires relatively expensive high-current switches to provide power to a window motor via mechanical contacts. It also necessitates the use of thicker gage wires, adding to both the cost and weight of the wire harness used in such a system. And third, in high-current switch systems, there is significant voltage drop as the current flows from the driver door to the passenger's window motor. In some vehicles, this results in passenger's window operating at a noticeably slower rate than the driver's window. The voltage drop may be lessened by using larger gage wire, but this would increase both cost and weight.
Lastly, existing designs, typified by the circuit shown in FIG. 1, require that the power wires to the passenger's window motor be run through the driver's switchplate. This requires more wiring and splices (thus increasing both circuit cost and circuit complexity) than if the power wires were directly supplied to the passenger's window motor.